Wear element for screw presses or the like

ABSTRACT

A wear element comprising a wear plate of a hard, typically ceramic material, locked in a dovetail recess of a bracket made of steel. The bracket consists of two initially separate parts comprising a respective one of the two inclined dovetail wedge surfaces of the dovetail recess. The two parts are welded together when positioned with their respective wedge surfaces tightly engaging a respective one of two complementary inclined surfaces formed on the wear plate.

BACKGROUND OF THE INVENTION

The invention relates to a wear element intended to be mounted along ascrew wing of a screw press or the like, comprising a wear plate of ahard, typically a ceramic, material locked in a dovetail recess formedin a steel bracket.

In operation of screw presses, such as in the paper and celluloseindustry, sugar production etc, a screw rim is subject to very highwear. In order to reduce a similar problem in connection withcentrifuges, special wear elements of the above kind have been proposedin GB 2 048 728 and DE 2 556 671. These prior structures, in which thewear plate is mounted in its bracket by being pushed into a preformeddovetail slit, require accurate machining and adjustment of the parts inorder to obtain a stable and rigid locking of the wear plate in thedovetail slit. Thus, a considerable amount of diamond grinding of thevery hard ceramic material will be necessary, with corresponding highcosts of manufacture of the prior wear elements. As an alternative, thewear plates may be locked by through-going fasteners, but a suchapproach would reduce the functioning and life of the wear elements.

Among the various embodiments disclosed in the above GB 2 048 728 thereare some in which the wear plate may be locked in its bracket by meansof a wedge member abutting a rear or radially inner, canted surface ofthe wear plate and welded in place on the bracket. Although apparentlynot recognized in the specification of the GB publication, such approachcould be adapted to permit the ceramic wear plate to be used "raw"directly from the furnace, without the necessity of any diamond grindingfor dimensional adjustments. By locking or securing the ceramic plate toits bracket in this manner, rather than having to push it into apreformed slit in the bracket as in the other prior embodiments, a rigidand very strong locking of the wear plate in the bracket would beachieved, independently of any irregularities or inaccuracies in shapeand dimensions of the ceramic wear plate.

On the other hand, in the above prior wedge member embodiment, the wedgemember together with parts of the bracket located between the screw huband ceramic wear plate will be exposed to the material conveyed throughthe apparatus. This is of minor concern in the prior GB 2 048 728apparatus, since it is of the centrifuge type in which the abrasivematerial, in operation of the centrifuge, is concentrated along the rimof the screw wing or flight, while the radially inner portion of thewing is not. In screw presses on the other hand, such as used in thecellulosic industry, the entire radial extent of the wing is subject toheavy abrasive action and therefore, if the screw wing is to beprotected by ceramic wear plates, it would be essential to have theportion of the screw wing intermediate the screw hub and ceramic wearplate as narrow as possible, especially in the converging compressionportion of the press where the abrasion is at a maximum, as otherwisethe unprotected intermedate portion would rapidly cave owing to theabrasive material filling the space between succesive screw wings.

SUMMARY OF THE INVENTION

The present invention, in addition to advantageously permitting the useof "raw" ceramic plates, solves this problem by providing a wear elementintended to be mounted along the screw wing of a screw press or thelike, comprising a wear plate of a hard, typically a ceramic, material,and comprising further a steel bracket, the wear element being locked ina dovetail connection recess in the steel bracket; the bracket beingmade up of two parts, each providing a respective one of two wedgesurfaces of the dovetail connection recess; the wear element beingformed with a back portion having wedge surfaces complementary to thewedge surfaces of the bracket parts and having side surfaces; bothbracket parts each having a channel-like indentation whose bottom formsa respective one of the wedge surfaces of the dovetail connectionrecess, and legs of the channel-like indentations of one bracket partbeing welded to legs of the other bracket part along a welding grooveextending on either side of the recess.

The term "welding" as used herein is to be understood in a broad senseincluding brazing, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings in which:

FIGS. 1a-2d are a side view, top plan view, end view and bottom planview respectively of a wear element according to the invention,

FIGS. 2a-2d are a side view, plan view and end view respectively of awear plate to be used in the wear element according to the invention,

FIGS. 3a-3d are a sectional view, plan view and end view respectively ofa bracket for holding the wear plate, and

FIG. 4 is a plan view of a slightly modified embodiment of the bracket.

DETAILED DESCRIPTION OF THE INVENTION

The wear element shown on FIGS. 1a-1d consists of a wear plate 2 of ahard material such as ceramics, rigidly locked in a dovetail recessformed in a bracket 1 made of steel.

As best shown in FIGS. 2a-2c the wear plate 2 includes a trapezoidalbody portion 9 with an unbroken wear surface 10 and a back portion 3opposite the wear surface 10. The back portion 3 is shown as arectangular, preferably substantially square protrution of a smallersize than body portion 9 and formed with opposite, inclined wedgesurfaces 4', 4" for engaging complementary inclined wedge surfaces ofthe bracket recess, and parallel straight (i.e. substantially normal tothe wear surface) side surfaces 12. The body portion 9 advantageouslyhas a slightly curved front edge 13 of a curvature adapted to a screwrim to which the wear element is to be mounted, and slightly rearwardlyconverging side edges 14 for engaging side edges of adjacent wearelements upon mounting onto the screw rim. In the example shown the onewedge surface 4' of the back portion and two side surfaces 12 thereofare offset relative to the front edge 13 and two side edges 14respectively of the body portion 9, while the second wedge surface 4" ofthe back portion with a correspondingly inclined rear edge 15 of thebody portion 9.

Preferably, the bracket 1 is made of stainless steel. As shown in FIGS.3a-3c according to an important feature of the invention, it isinitially formed in two separate parts 6' and 6", adapted to be weldedtogether around the back portion 3 of the wear plate 2. In the exampleshown the bracket 1, like the wear plate 2, is a substantiallytrapezoidal plate having a curved front edge 16 and converging sideedges 17 which, upon assembly, generally coincide with the front edge 13and side edges 14 respectively of the wear plate.

Each bracket part 6', 6" is provided with a channel-like indentation19', 19" which, in the assembled (but yet not welded) state of thebracket parts shown in FIGS. 3a-3c together form a substantially squarerecess or opening 20 formed as a dovetail slit having opposite inclinedwedge surfaces 5', 5" respectively corresponding to the wedge surfaces4', 4" of the wear plate back portion 3 and having straight end surfaces18 corresponding to the straight side surfaces 12 of the back portion.Thus, the bottom surface of the indentations 19', 19" of the bracketparts 6', 6" respectively each form one of the wedge surfaces 5', 5" ofthe dovetail recess 20.

The wear element according to the invention as shown in FIGS. 1a-1d isimplemented by positioning the two separate bracket parts 6', 6" withtheir respective wedge surfaces 5', 5" tightly pressed againstrespective wedge surfaces 4', 4" of the wear plate back portion 3, andthen welding the two bracket parts 6', 6" together along a weldinggroove 8 which, in the example shown in FIGS. 1a-1d and 3a-3c extends oneither side of the recess 20 along a line parallel to and preferablysubstantially centrally between the wedge surfaces 5', 5". As a resultthe wear plate will be immovably locked between the wedge surfaces 5',5" and end surfaces 18 of the bracket parts. Preferably, to furtherstrengthen the relative immobility of the wear plate and bracket, anadhesive 7 may be applied at least between the bottom surface of thewear plate body portion 9 and top surface of bracket 1.

Advantageously, as shown in FIGS. 1a and 3a, one of the brackets 6" mayhave a thickened end portion 21 with a shoulder 22 aligned with thebracket wedge surface 5" to engage rear surface 15 of the wear platebody portion 9 aligned with the wedge surface 4" of the wear plate backportion 3, for providing additional support to the wear plate.

FIG. 1a also illustrates how wear elements of the invention can bewelded to a screw wing 23 of a screw 24 shown in phantom lines, by frontweld 25 and rear weld 26.

The bracket 101 shown in FIG. 4 differs from bracket 1 of FIGS. 3a-3c,only by the welding grooves 108 formed by the assembled bracket parts106', 106" extending normal rather than parallel to the bracket top andbottom surfaces on each side thereof.

I claim:
 1. Wear element intended to be mounted along the screw wing ofa screw press or the like, comprising a wear plate of a hard, typicallya ceramic, material, and comprising further a steel bracket, said wearplate being locked in a dovetail connection recess in said steelbracket; said bracket being made up of two parts, each providing arespective one of two wedge surfaces of said dovetail connection recess;said wear plate being formed with back portion having wedge surfacescomplementary to said wedge surfaces of said bracket parts and havingside surfaces; both said bracket parts each having a channel-likeindentation whose bottom forms a respective one of said wedge surfacesof said dovetail connection recess, and legs of said channel-likeindentations of one bracket part being welded to legs of the otherbracket part along a welding groove extending on either side of saidrecess.
 2. Wear element according to claim 1, wherein said weldinggroove extends along a line substantially centrally between said wedgesurfaces of said the dovetail recess.
 3. Wear element according to claim1, wherein said welding groove extends across either side edge of saidbracket, and preferably centrally relative to said bracket wedgesurfaces.
 4. Wear element according to claim 1, wherein said wear plateis formed with a substantially trapezoidal body portion having anunbroken wear surface opposite said back portion, and side surfaces ofsaid back portion and at least one wedge surface thereof being staggeredrelative to side and front edges respectively of said body portion. 5.Wear element according to any one preceding claim 1, wherein one bracketpart is formed with a thickened end portion with a shoulder in alignmentwith said bracket wedge surface to engage a rear surface of said bodyportion aligned with said wedge surface of said back portion.